rtlwifi: fix broken VHT support

When using a 5G-capable device with VHT (802.11ac) rates enabled was not
working (packets were not delivered) and the following mac80211 warning
was printed:

WARNING: CPU: 3 PID: 2253 at net/mac80211/rate.c:625 ieee80211_get_tx_rates+0x22e/0x620 [mac80211]()
Modules linked in: rtl8821ae btcoexist rtl_pci rtlwifi fuse drbg ansi_cprng ctr ccm bnep bluetooth af_packet nfs fscache vboxpci(O) vboxnetadp(O) vboxne
tflt(O) vboxdrv(O) arc4 snd_hda_codec_generic x86_pkg_temp_thermal rtsx_pci_sdmmc mmc_core rtsx_pci_ms kvm_intel memstick iwlmvm kvm mac80211 snd_hda_intel snd_hda_cod
ec snd_hwdep snd_hda_core irqbypass snd_pcm iwlwifi crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel aes_x86_64 snd_timer lrw gf128mul glue_h
elper ablk_helper cryptd snd cfg80211 pcspkr serio_raw e1000e rtsx_pci lpc_ich ptp xhci_pci mfd_core pps_core xhci_hcd soundcore toshiba_acpi thermal sparse_keymap wmi
 toshiba_bluetooth rfkill acpi_cpufreq battery ac processor dm_mod i915 i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops
drm sr_mod cdrom video button sg autofs4 [last unloaded: rtlwifi]
CPU: 3 PID: 2253 Comm: Timer Tainted: G        W  O    4.5.0-rc1-wl+ #79
Hardware name: TOSHIBA TECRA A50-A/TECRA A50-A, BIOS Version 4.20   04/17/2014
  ffffffffa05c4be6 ffff8802262036d8 ffffffff813d7912 0000000000000000
  ffff880226203710 ffffffff8106bcb6 ffff8800c6831300 ffff8800c6831330
  0000000000000000 ffff8800c683133c ffff880065923638 ffff880226203720
Call Trace:
  <IRQ>  [<ffffffff813d7912>] dump_stack+0x4b/0x79
  [<ffffffff8106bcb6>] warn_slowpath_common+0x86/0xc0
  [<ffffffff8106bdaa>] warn_slowpath_null+0x1a/0x20
  [<ffffffffa05511ee>] ieee80211_get_tx_rates+0x22e/0x620 [mac80211]
  [<ffffffffa0782232>] ? rtl_is_special_data+0x32/0x240 [rtlwifi]
  [<ffffffffa055209e>] ? rate_control_get_rate+0xce/0x150 [mac80211]
  [<ffffffff810bfc7d>] ? trace_hardirqs_on+0xd/0x10
  [<ffffffff81071cc5>] ? __local_bh_enable_ip+0x65/0xd0

Signed-off-by: Kalle Valo <kvalo@codeaurora.org>